Alternating-current electromagnet.



D. L. LINDQUIST. ALTERNATING CURRENT BLBOTROMAGNET. AIP'LIOATION FILED PEB.9, 1910.

1,005,856. Patented Oct. 17, 1911.

UNITED STATES PATENT 4ourlet.

DAVID Il. LINDQUIST, OF YONKEBS, NEW YORK, ASSIGNOR TO OTIS ELEVATOR COMPANY, A CORPORATION OF NEW JERSEY.

ALTERNATING-CURRENT ELECTROMAGN ET.

Specification of Letters Patent. i Patented Oct. 17, 1911.

Application filed February 9, 1910. Serial No. 542,817.

To all whom t't may concern:

Be it known that I, DAVID L. LINDQUIST, a subject of the King of Sweden, residing at Yonkers, in the county of 'Westchester and State of New York, have invented a certain new and useful Improvement in Alternating-Current Electromagnets, of whichthe following is a specification.

The invention is an alternating current electro-magnet comprising primary and secondary circuits wherein the currents differ in phase, so that at no instant is the resultant magnetic traction reduced to zero. In circuit with the secondary is an ohmic resistance, or an ohmic resistance and a capacity, by adjustment of which maximum traction is obtained and the phase angle between the fluxes is approximated as near as possible to ninety degrees. As a consequence, the armature is-held to the magnet with a constant and maximum pull, whereby chattering of said armature due to curren alternations is prevented.

The accompanying drawing is a diagram, showing the magnet and its connections.

A is the magnet vcore having at its polar extremity three legs B, C, D. The primaryl coil E which surrounds the body of the magnet is Ato be connected with any suitable source of alternating current by* the con-;

ductors F, between which andl said coil any suitable circuit closing switch G may be interposed.

A secondary coil H surrounds the middle leg C, and includes Ian ohmic resistance I and a condenser J. The condenser J, under circumstances hereinafter explained, may be omitted, the circuit then'proceeding as indicated by dotted lines at K. So also, under certain conditions, the resistance I may be omitted, leaving only the condenser in circuit. 4

lVhen the primary coil E is energized by an alternating current, the secondary current caused in the coil H produces an electro-b mptive force which throws the ma etization Vof legs B and D outAof phase with that of leg C. Hence minimum and maximum` traction of legs B, D upon an armature, asv L, does not synchronize with the minimum and maximum traction of leg C. Hence the resultant mechanical effort upon' the armature will never be zero'at any instant, and hence the armature will beheld to the magnet core without chattering due to the current alternations. v

In order to obtain a constant magnetic pull, it is obvious that the ideal phase angle between the primary and secondary fluxes 1s 90, when the magnet becomes the same as a two phase magnet. It is desirable, therefore, to bring the phase angle between the fluxes to as near an approximation to 90 as possible. Thisis the function of the capaclty J introduced into the secondary circuit, 1n' connection with the resistance I.

With said resistance arbitrarily selected at the outset, the. amount of capacity required can be readily determined from the followmg data: (l) the reluctance of the two magnetlc circuits, (2) the iron losses \in the circuits and (3) the self induction andreslstance of the primary and secondary coils. t When resistance is used alone, without'the introduced capacity, its amount may also be. determined .from the above data. In th1s way it is possible from a predetermined current to obtain the highest possible minimum pull for the whole magnet.

Generally speaking, the geometrical sum of the resistance and capacity must be suchv as to allow a current in the secondary core sutlicient to give a flux which will cause the.

same pull by the secondary magnet circuit as by the primary magnet circuit, and the relation between the resistance and capacity must be such as to give as near an approximation as possible to 90 phase difference between the primary and secondary fluxes.

While this electro-magnet is more especially intended to give constant pull, it may be used in circumstances where constant pull is not desired, but where the object is a very small current expenditure. -In such event, the capacity J only may be introduced in the secondary circuit. The condenser current then flows partly inthe opposite direction to the magnetizing current, and therefore the resultant current may, underl favorable conditions, be considerably' less .than the magnetizing current aloneiron losses not beingconsidered. Theoretically with no losses in the system, the resultant current may be zero, which is, of

course, practically unattainable.

The secondary coill C is preferably of copper wire, so as to reduce space and heating 4within the magnet.

I claim: 1. An alternating current electro-magnet comprising conduetively independent primary and secondary circuits, means for causing the magnetic fluxes due to the currents in said circuits to differ in phase, and a selected ohmic resistance interposed in said secondary circuit.

2. An alternating current electro-magnet comprising conductively independent -primary and secondary coils, means for causing the magnetic fluxes due to the currents in said coils to differ in phase, and a selected ohmic resistance external to said secondary coil a'nd interposed in the circuit thereof.

3. An alternating current electro-magnet comprising` primary and secondary circuits', means for causing the magnetic uxes dueto the currents in said circuits to differ in phase, and a selected capacity interposed in said secondary circuit.

4. An alternating current electro-magnet comprising primary and secondary circuits, means for causing the magnetic fluxes due to the currents in said circuits to differ in phase, and an ohmic resista-nce and a selected capacity interposed in said secondary circuit.

5. An alternating current electro-magnet comprising primary and secondary coils, means for causing the magnetic fluxes due to the currents in said coils to dier in phase, and a selected ohmic resistance and a selected capacity external to said secondary coil and in circuit therewith.

In testimony whereof I have afiixed my signature in presence of two Witnesses.

DAVID L. LINDQUIST. 

